1. Field of the Invention
The invention relates to a method and to an apparatus for monitoring the heat transfer and thus the efficiency of a condenser.
The efficiency of condensers in power stations is mainly dependent on the heat transfer from the steam, via the condenser tubes into the cooling water, which is once again decisively influenced by the degree of contamination of the tubes as a result of deposits or corrosion. The measurement of the actual heat transfer on a condenser is difficult if it shall be accurate and shall reveal at an early stage any deterioration before any detectable performance decrease occurs. The usual method of monitoring a condenser by measuring the steam temperature or steam pressure, the cooling water inlet and outlet temperature, as well as the condensate quantity flow and also the cooling water flow is too imprecise in order to detect at an early time contaminations of the tubes.
The high performances of modern power station units lead to high steam and cooling water flows with correspondingly large cross-sections of the cooling water and steam paths, which require an accurate measurement of the temperature and speed distribution in said cross-sections, in order to make it possible to obtain an adequately precise information of the effective mean values.
This method is not particularly accurate, because over and beyond it numerous other parameters also influence the efficiency, so that all that can be established therewith is the deterioration when it has reached an alarming extent. Therefore the condenser cleaning system, which keeps the condenser tubes clean by means of circulating elastic cleaning members is consequently operated more on the basis of general empirical values than the specific needs of the individual power plants. In many cases this is sufficient to obtain a satisfactory condenser state, but in other cases leads to "undercleaning", i.e. to deposits, or to "overcleaning", i.e. to corrosion in the case of copper alloys. Thus, an optimum operation of the condenser through an optimum cleaning using this method of standard operation supervision alone is not possible.
2. Description of the Related Art
From the German publication 37 05 240.3 a measuring method is known, in which one or more condenser tubes of a condenser are concretely measured with respect to the cooling water inlet temperature, the outlet temperature and the flow velocity, the steam temperature being measured on an adjacent tube which is shut down. The advantage is that a direct measurement takes place on a tube actually participating in the condensing of steam, so that it is possible to exclude marginal conditions, which can otherwise occur in special tubes separated for the measurement of bypass-operated model condensers. For determining the cooling water flow velocity, either foreign substances, such as saline solutions or the like are added to the cooling water at the tube inlet, or marked sponge rubber balls are used. The flow velocity in the tube is determined from the passage time established by corresponding sensors. Both measuring methods require a relatively high expenditure, so that certain difficulties are to be expected in the acceptance of such installations.
An attempt has also been made to determine the degree of contamination of the condenser tubes by measuring the pressure drop from the inlet side to the outlet side. However, it has been found that there are rough and smooth impurities, which differently influence the pressure drop, so that by using such a differential pressure measurement it is not possible to obtain sufficiently accurate information on the heat transfer.